A High Sensitivity Measurement of the MeV Gamma-Ray Spectrum of Cygnus X-1

Abstract

The Compton Gamma-Ray Observatory (CGRO) has observed the Cygnus region on several occasions since its launch in 1991. The data collected by the COMPTEL experiment on CGRO represent the most sensitive observations to date of Cygnus X-1 in the 0.75-30 MeV range. A spectrum accumulated by COMPTEL over 10 weeks of observation time shows significant evidence for emission extending out to several MeV. We have combined these data with contemporaneous data from both BATSE and OSSE to produce a broad-band gamma-ray spectrum, corresponding to the low X-ray state of Cygnus X-1, extending from 50 keV up to approximately 5 MeV. Although there is no evidence for any broad line-like emissions in the MeV region, these data further confirm the presence of a hard tail at energies above several hundred keV. In particular, the spectrum at MeV energies can be described as a power-law with a photon spectral index of $\alpha$ = -3.2, with no evidence for a cutoff at high energies. For the 200 keV to 5 MeV spectrum, we provide a quantitative description of the underlying electron spectrum, in the context of a hybrid thermal/non-thermal model for the emission. The electron spectrum can be described by a thermal Maxwellian with a temperature of $k{T}_e$ = 86 keV and a non-thermal power-law component with a spectral index of $p_e$ = 4.5. The spectral data presented here should provide a useful basis for further theoretical modeling.

28 pages, 6 figures, accepted for publication in ApJ. Considerably revised from original submission

References in corpus (15)

• Spectral Properties of Accretion Disks Around Galactic and Extragalactic Black Holes
• The Two-Phase Pair Corona Model for Active Galactic Nuclei and X-ray Binaries: How to Obtain Exact Solutions
• Simultaneous X-ray and gamma-ray observations of Cyg X-1 in the hard state by Ginga and OSSE
• Gamma-Ray Spectral States of Galactic Black Hole Candidates
• Self-Consistent Thermal Accretion Disk Corona Models for Compact Objects: II. Application to Cygnus X-1
• Stochastic Particle Acceleration near Accreting Black Holes
• Self-Consistent Thermal Accretion Disk Corona Models for Compact Objects: I. Properties of the Corona and the Spectrum of Escaping Radiation
• Electron Acceleration and the Production of Nonthermal Electron Distributions in Accretion Disk Coronae
• Gamma-rays from Galactic Black Hole Candidates with Stochastic Particle Acceleration
• Thermal Comptonization in Mildly Relativistic Pair Plasmas
• High-Energy Spectral Complexity from Thermal Gradients in Black Hole Atmospheres
• A fit to the simultaneous broadband spectrum of Cygnus X-1 using the transition disk model
• A Self-Consistent Model For The Long-Term Gamma-Ray Spectral Variability of Cygnus X-1
• The Spectral Variability of Cygnus X-1 at MeV Energies
• A Thermal-Nonthermal Inverse Compton Model for Cyg X-1

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